Due to events such as caries, loose fillings, trauma and infection, the pulpa (i.e., the dental pulp) of living teeth can often become inflamed. In most cases such inflammation is irreversible, and as a result the affected pulpa must be removed by a dentist. In addition to the pulpa, bordering infected hard tissues must also be removed. The cavities formed by the removal of such pulp and tissue (i.e., a root canal operation) must be tightly sealed. To achieve this end, there are marketed a number of products which comprise zinc oxide or calcium hydroxide in combination with an organic salt former. However, none of these marketed materials have completely or satisfactorily met the requirements of a root canal filling material.
Root canal filling materials must form tight seals in order to prevent an invasion into the canal of infectious germs. For example, after root canal operations, there is often a danger of maxillary infection. A high degree of histocompatibility is also required in a filling material, because the filling materials upon emerging from the dental root tip can come into contact with living tissue. Moreover, for maintaining tightness, the root canal filling materials should display only a very slight solubility. Finally, so as to allow for their introduction into narrow root canals, a suitable processing time and viscosity should also be possessed by the filling materials.
In order to increase the sealing tightness of filling materials previously utilized, and in order to compensate for shrinkage during hardening reactions, formable filling materials have frequently been used as sealants in combination with thin pegs made from gutta-percha (i.e., a filled, natural resin material). For example, in one textbook method, many such pegs are laterally condensed in a filling process, so as to keep the proportion of formable filling material used as low as possible. The method is extremely time consuming.
Glass ionomer cements are known for their ability to form tight edge seals (e.g., they display a chemicophysical adhesion to the dental substance). Furthermore, they show only very slight solubility and are categorized as histocompatible. Even so, they lack a sufficient processing time for introduction into a root canal. In conventional application areas for glass ionomer cements (e.g., dental fillings, securing cements, sealant materials and stump reconstruction materials) the cements' required processing times were only two to three minutes. For the filling of root canals (including the necessary X-ray check), however, a dentist needs about ten minutes of processing time. Additionally, the viscosities of the glass ionomer cements are often too high for their introduction into a root canal by conventional means. That is, the pastes formed therewith are too thick or solid. Moreover, when glass ionomer cement systems have been diluted, this has led to materials having high solubilities.
U.S. Pat. No. 4,861,808 discloses glass ionomer compositions which contain a light metal fluoride, namely strontium fluoride, which is used to make dental fillings X-ray visible. The X-ray opacity and the processability of the produced compositions are, however, not satisfactory.
U.S. Pat. No. Re. 33,100 describes glass ionomer compositions which, to prevent irritation of the dental pulp, are buffered with 5 to 20% by weight of a soluble heavy metal oxide, namely zinc oxide, and 0 to 10% by weight titanium dioxide. The processability of these compositions and the durability of dental fillings made therewith have not heretofore been satisfactory.